More than half of all end-stage kidney disease (ESRD) patients are now over the age of 65. The fastest growing population on the kidney transplant waiting list is the elderly. Elderly patients on the transplant waiting list are vulnerable to declining health and an increasing mortality rate while on the waiting list. Consequently, there has been a substantial rise in the use of older donors, both living and deceased, in their 7th of 8th deceases. Older donors, whether deceased of living, have been reluctantly used for kidney transplantation because survival from of a kidney transplant from an aging donor is much shorter than from a younger donor. This age group is prone to an insidious renal vasculopathy and glomerulopenia, superimposition of with on a single, senescent kidney could result in the remnant kidney phenomenon with progressive chronic kidney disease. By year 05 of this grant, I will complete recruitment into a longitudinal study of a group (N=30) of aging, living donors (>55 years). A matching group of youthful living donors (<45 years) will serve as controls. I will also initiate a cross-sectional study of older living donors who donated a kidney 10-20 years ago at age > 55 years to evaluate longer term outcome. In addition to elucidating the pathophysiology of chronic kidney disease in older donors who have undergone kidney donation, my goal is to conduct a detailed study of renal senescence in healthy older individuals who undergo the process of kidney donation and to use the information gained in this study to establish evidence-based guidelines for organ allocation in the elderly. The largest increase in the incidence of ESRD is in the population over 65, with a parallel increase in the elderly awaiting kidney transplant. Even larger numbers of elderly persons have CKD not requiring dialysis. A central question in chronic kidney disease will shift toward the care of the elderly. My goal is to determined evidence-based guideline for selection of elderly individuals for safe transplantation and donation.